Improvement of molecular beam epitaxy-grown low-temperature GaAs through pdoping with Be and C

Nonstoichiometric GaAs thin layers can be produced in molecular beam epitax y if they are grown at temperatures below 400 degrees C [low-temperature (L T)-GaAs]. Due to the incorporation of excess As in the form of native point defects, namely As antisite defects (As-Ga). these layers exhibit ultrasho rt time response and, after annealing at 600 degrees C, excellent semi-insu lating behavior. The ultrashort time response, however, is governed by the concentration of ionized antisites ([As-Ga(+)]), which are just a few perce nt of the total concentration of antisites ([As-Ga]) Additionally, thermal annealing leads to As precipitate formation and out-diffusion of point defe cts into adjacent layers. Recent studies have shown that p-type doping with Be increases the thermal stability of point defects and shortens the time response due to an increase in ionized antisites, while maintaining the hig h electrical resistivity in as-grown material. We report on the studies of p doping of LT-GaAs with Be and, alternatively, with C in order to enhance the thermal stability in semi-insulating thin layers with ultrashort carrie r trapping times. The epilayers were characterized and their electronic pro perties investigated by time-resolved reflectivity transients and Hall meas urements. The properties of as-grown and annealed thin layers will be discu ssed based on the results of defect concentrations. These results will be c ompared to those obtained in undoped LT-GaAs. (C) 1999 American Vacuum Soci ety. [S0734-211X(99)05603-6].